Rusted eyelets on DT Swiss rim

At the weekend I found a large amount of bubbling around the valve and rust around 80% of the eyelets on the rim of my M1600 wheel.. Has this happened to anyone else ? On this rim or any others ?
The wheel is 18 months old and has been generally cared for and always stored indoors... I have been mountain biking for 20 years and had many pairs of wheels and have never had this problem before. Have I just been lucky or is this crap manufacturing ?
Thoughts most welcome